Perimetry is a procedure to examine a visual field of a person. The visual field of a single eye thereby extends towards the temple up to approx. 90 degrees, towards the nose and upwards to about 60 degrees and downwards to about 70 degrees. The different expansion is provided by the protected location of the eye in the eye socket. Towards the nose, the nasal bridge restricts the visual field, upwards and downwards the orbital margin, while the side of the temple is essentially free.
The visual field of the right and left eye overlaps in the middle. This overlapping covers an angle of about 120 degrees. A depth perception (stereo vision) is only possible in the area of the overlap.
In perimetry, light stimuli are then usually provided by a special device (perimeter) in different areas of the visual field of a person to be examined, while the person focuses her eyes or an eye to be examined on a fixed point and evaluates a reaction of the person (e.g. a confirmation of the perception of the light stimulus). Such light stimuli may have different brightness levels.
Such conventional perimeters require a lot of space, are comparatively expensive, and/or require skilled personnel to operate them.